Semiconductor devices are used in a variety of electronic applications, such as personal computers, cell phones, digital cameras, and other electronic equipment, as examples. Semiconductor devices are typically fabricated by sequentially depositing insulating (or dielectric) layers, conductive layers, and semiconductive layers of material over a semiconductor substrate, and patterning the various layers using lithography to form circuit components and elements thereon.
A transistor is an element that is utilized extensively in semiconductor devices. There may be millions of transistors on a single integrated circuit (IC), for example. A common type of transistor used in semiconductor device fabrication is a metal oxide semiconductor field effect transistor (MOSFET), as an example.
Early MOSFET processes used one type of doping to create either positive or negative channel transistors. More recent designs, referred to as complimentary MOS (CMOS) devices, use both positive and negative channel devices, e.g., a positive channel metal oxide semiconductor (PMOS) transistor and a negative channel metal oxide semiconductor (NMOS) transistor arranged in complimentary configurations. An NMOS device negatively charges so that the transistor is turned on or off by the movement of electrons, whereas a PMOS devices involves the movement of electron vacancies. While the manufacture of CMOS devices requires more manufacturing steps and more transistors, CMOS devices are advantageous because they utilize less power, and the devices may be made smaller and faster.
There is a trend towards reducing the size of semiconductor devices in the industry. However, manufacturing challenges are introduced as the dimensions of the various material layers are decreased, and patterning the material layers in smaller and smaller dimensions is also problematic.
Another trend in the semiconductor industry is the use of high dielectric constant (k) dielectric materials for a gate dielectric material of transistors. High k dielectric materials have a dielectric constant of greater than about 4.0, e.g., greater than the dielectric constant of SiO2, which has been used as a gate dielectric material of transistors for many years. Because of their increased insulative properties, high k dielectric materials may be used in thinner dimensions than SiO2 in transistor applications. However, the use of high k dielectric materials results in undesirable effects on the transistor, to be described further herein.
Thus, what are needed in the art are improved transistors and methods of manufacture thereof.